Wireless Power Transfer (WPT) enables supplying power through an air gap, without the need for current-carrying wires. WPT can provide power from an AC source to a compatible device without physical connectors or wires. WPT can recharge many devices, such as portable communication devices including mobile phones, tablets, and other electronic devices. WPT can use electromagnetic fields created by charged particles to carry energy between transmitters and receivers over an air gap. The air gap is bridged by converting the energy into electromagnetic (EM) waves such as radio waves, microwaves or even light that can travel through the air. The electromagnetic waves are transmitted over the air, and are then received and converted into usable electrical current by a wireless power receiver.
In wireless power receivers, a rectifier circuit can be used to convert inductively coupled AC power from a receive coil into the DC power needed by the receiver subsystem. In a typical implementation an integrated rectifier may include four power field-effect transistors (FETs) used in an H-bridge configuration around a receive coil. Internal comparators may monitor the AC signal and turn the FETs on and off accordingly. For maximum efficiency, the threshold setting may be set such that the FETs can turn on and off quickly. The key challenge for the integrated rectifier is to accurately sense the AC signal and reliably turn on and off in the presence of system noise and ringing due to resonances of the receive coil.